Unidirectional breather means for electrical apparatus



Dec. 9, 1969 w, E HARPER 3,483,306

UNIDIRECTIONAL BREATHER MEANS FOR ELECTRICAL APPARATUS Filed Dec. 22, 1967 POWER 34 SOURCE 4O 18/ POWER N SOURCE United States Patent 3,483,306 UNIDIRECTIONAL BREATHER MEANS FOR ELECTRICAL APPARATUS William E. Harper, Walpole, Mass., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Dec. 22, 1967, Ser. No. 692,878 Int. Cl. H01b 9/06 U.S. Cl. 174-14 5 Claims ABSTRACT OF THE DISCLOSURE The tank for an electric circuit breaker contains a quantity of oil and has an airspace above the oil surface. An air inlet tube is provided in the tank immediately above the oil surface and an air outlet tube is provided in the tank above the air inlet tube. A thermostatically controlled electrical heater is located inside the tank just below the oil surface to heat the oil and drive moisture out of the oil, into the airspace and, as a result of air circula tion, out the air outlet tube. In another embodiment, a convection tube is located in the oil and has an auxiliary electric heater at its bottom end to effect convection and improve circulation of the oil throughout the tank.

SUMMARY OF THE INVENTION This invention relates generally to unidirectional breather means for liquid cooled and insulated electrical apparatus such as circuit breakers, transformers and the like. More particularly, it relates to unidirectional breathers which employ heaters for the liquid to drive off contaminating moisture from the liquid and effect air circulation.

'Prior art unidirectional breathers, such as the type shown in U.S. Patent No. 2,000,862; issued May 7, 1935 to L. C. Nichols and assigned to the same assignee as the present application, employed a tank having electrical apparatus therein, insulating and cooling liquid such as oil in said tank with an airspace above the liquid, an air outlet in the tank located above the liquid level and communicating with the airspace and with the atmosphere, and an air inlet in the form of a pipe which communicated with the airspace and with the atmosphere but which extended through the liquid whereby incoming air was heated by the liquid. Heating of the incoming air caused air circulation in the airspace above the liquid and a continuous flow of moisture laden air was driven from the air outlet. Unidirectional breathing apparatus as aforedescribed is satisfactory for its intended purpose but in order to operate, it requires that the liquid be maintained at temperatures above atmospheric temperature by the apparatus immersed in the liquid. This only occurs if the apparatus opeartes at relatively high temperatures.

A unidirectional breather in accordance with the Nichols patent is of very limited effectiveness in present day large oil type circuit breakers, for example, where cooling is more efiicient and where little heat is generated during periods of light loading. Therefore, in accordance with the present invention, thermostatically controlled heating means, preferably electric, are provided near the upper surface of the oil to maintain control of the dielectric strength of the oil by driving water vapor therefrom. In accordance with a further aspect of the invention, a convection tube is located in the oil and an auxiliary heater is applied near the lower oil inlet end of the tube to effect improved oil circulation by convection of the oil throughout the tank.

OBJECTS It is an object of the present invention to provide improved unidirectional breather means for liquid cooled and insulated electrical apparatus such as oil circuit breakers.

Another object is to improve unidirectional breather means of the aforesaid character which are advantageously employed in apparatus which operates near atmospheric temperatures either continually or during periods of light loading.

Another object is to provide unidirectional breather means of the aforesaid character which are thermostatically controlled so as to be operative only when needed.

Another object is to provide unidirectional breather means of the aforesaid character which employs auxiliary heating means to effect improved liquid circulation within the apparatus tank.

Other objects and advantages of the invention will hereinafter appear.

DRAWINGS The accompanying drawings illustrate two preferred embodiments of the invention, but it is to be understood that the embodiments illustrated are susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawings:

FIG. 1 is a side elevational view, partly in cross section, of electrical apparatus, such as an oil circuit breaker, incorporating unidirectional breather means in accordance with the present invention; and

FIG. 2 is a view similar to FIG. 1 of a portion of the oil circuit breaker of FIG. 1 showing it incorporating unidirectional breather means in accordance with another aspect of the present invention.

DESCRIPTION OF THE INVENTION Referring to FIG. 1 of the drawings, the numeral 10 designates an electrical device, such as an oil circuit breaker, incorporating unidirectional breather apparatus in accordance with the present invention. Circuit breaker 10 comprises a tank 12 which is filled with electrical insulating and cooling liquid 16, such as oil, to a level 18 and an airspace 20 exists thereabove. A pair of bushings 22 and 24- are provided in a cover 14 of tank 12 to adapt circuit breaker 10 for line connection and arc interrupters 26 and 28 are mounted on the bushings 22 and 24, respectively. The are interrupters 26 and 28 are understood to comprise stationary contacts (not shown) which are bridged by a movable crosshead 30 when the circuit breaker is closed, as shown in FIG. 1. As will be understood, the bushings 22 and 24, the arc interrupters 26 and 28, and crosshead 30 are electrically conductive and also, a source of heat when current flows therethrough and PR losses occur. Accordingly, they are submerged in liquid 16 for electrical insulating and for cooling purposes.

In accordance with the invention, air inlet means in the form of an air inlet tube 32 in tank 12 is provided for communication between airspace 20 and the outside atmosphere and is the means whereby atmospheric air enters tank 12. Air inlet tube 32 is located so that its interior opening is close to oil level 18.

Air outlet means in the form of an air outlet tube 34 is provided in tank 12 for communication between airspace 20 and the atmosphere outside the tank and is the means whereby air and water vapor are expelled from within the tank. Air outlet tube 34 is located so that its interior opening is higher than or above the interior opening of air inlet tube 32. The exterior opening of air outlet tube 34 is located away from the exterior opening of air inlet tube 32 so that recirculation of expelled air does not inadvertently occur.

A heater means in the form of a strip type electric heating element 36 is located in oil 16 as close as possible to oil level 18, i.e., the interface between the oil and the air in airspace 20, to effect heating of the oil and the air Wall of tank 12 and could be fabricated as one or several pieces. Heating element 36 is powered from a suitable power source 40 and is provided with thermostatic control means 42 which is located in the oil, for example, so as to sense the temperature thereof.

Circuit breaker and its breather means aforedescribed operate as follows. As will be understood, air in airspace 20 originates from the atmosphere and normally contains some water vapor. If this air is cooled below its dew point, moisture condenses on the inside wall of tank 12 and cover 14, sometimes causing rust and the rust and condensation drip into the oil contaminating it and creating a risk of insulation breakdown and arcing. In a device such as circuit breaker 10 wherein the oil temperature is low because of efficient design or light loading, oil temperature is not always high enough to maintain the air in airspace 20 at or above its dew point. Therefore, in accordance with the invention, when the temperature in oil 16 reaches a predetermined low temperature, thermostatic control means 42 senses this condition and connects heating element 36 to power source 40 and the oil at the oil-air interface is heated. This, in turn, elfects heating of the air at the oil-air interface. When the air is heated, its relative humidity drops and its moisture carrying capacity increases thereby preventing condensation. In addition, an air circulation pattern is established as the heated air rises and atmospheric air begins to flow into airspace 20 through air inlet tube 32 while air from airspace 20 begins to flow out to the atmosphere through air outlet tube 34. Cool ambient air entering inlet tube 32 is heated to prevent its relative humidity from dropping. In addition, the higher oil temperature and higher vapor pressure condition at the oil-air interface tends to drive off any moisture already in the oil near the surface thereof. Whenever the PR losses in the circuit breaker provide oil heating sufiicient to maintain air flow, to prevent moisture condensation from incoming air, and to drive off any water trapped in the oil near the surface thereof, thermostatic control means 42 senses this condition and turns olf heating element 36 to conserve energy. Thermostatic control means 42 turns on heating element 30 whenever conditions again warrant it.

Referring to FIG. 2, there is shown a modification to circuit breaker 10 in the form of means for providing circulation of the oil in tank 12 by convection so that oil from other regions in said tank is exposed to the higher temperature conditions being maintained at the oil-air interface, i.e., a region near the surface of said liquid. Such means take the form of a hollow tube 50 supported by tank 12 which is submerged in the oil so that its upper end or liquid outlet 52, although still submerged, is near the oil-air interface and its lower end or liquid inlet 54 is located near the bottom of the tank Where water condensate normally settles out and collects. Auxiliary heating means 56 are located near the lower end 54 of tube 50 to heat the oil near that end of the tube causing it to rise in the tube, flow out the upper end 52 of the tube, and establish an oil flow circulation pattern in tank 12.

The heat differential between the oil at the bottom and top of tube 50 must be such that oil will rise in the tube. Preferably, auxiliary heating means 56 is an electric heater which is electrically connected through thermostatic control means 42 to power source 40 and which turns on and off when heating element 36 is so operated. However, auxiliary heating means 56 could be connected so as to be in continuous operation. 1

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In combination,

an enclosed tank for electrical apparatus,

said tank containing a quantity of insulating liquid which tends to absorb water and having an airspace above the level of said liquid,

electrical apparatus in said liquid,

- air} inlet means in said tank above the level of said liquid communicating with the atmosphere outside said tank,

air outlet means in said tank above the level of said liquid and above said air inlet means communicating with the atmosphere outside said tank,

and heating means in said tank for heating said liquid near the liquid-air interface to a temperature higher than atmospheric temperature.

2. A combination according to claim 1 comprising thermostatic means for turning said heating means on and off as said liquid near said interface reaches predetermined temperatures.

3. A combination according to claim 1 including means for effecting circulation of said liquid in said tank to introduce liquid from other regions in said tank into a region near the surface of said liquid.

4. A combination according to claim 3 wherein said means for effecting liquid circulation comprises hollow tubular means in said tank, said tubular means having a liquid outlet located in said liquid near said interface and having a liquid inlet in said liquid below said liquid outlet, and means to effect liquid flow through said tubular means to effect liquid circulation.

5. A combination according to claim 4 wherein said means to effect liquid flow through said tubular means comprises auxiliary liquid heating means located near said liquid inlet of said tubular means.

References Cited UNITED STATES PATENTS 783,532 2/1905 Moody 219-209 X 2,000,862 5/1935 Nichols l74--l4 1,585,014 5/1926 Bucholz 200- X 1,591,163 7/1926 Greenwood 200150 LARAMIE E. ASKINS, Primary Examiner A. T. GRIMLEY, Assistant Examiner US. Cl. X.R. 

